1. Field of Invention
The present invention is directed to an electronic device. More particularly, the present invention is directed to a light-emitting device.
2. Description of Related Art
With advances in semi-conductor technology, light-emitting diodes have been widely used in our daily life because of having advantages like long lifetime, high switching speed, and small size.
FIG. 1 is a diagram illustrating an operating waveform of a light-emitting diode in prior art. As shown in FIG. 1, an input voltage Vin is a rectified AC voltage. When the input voltage Vin is greater than a threshold voltage Vhv of the light-emitting diode, the light-emitting diode is turned on and emits light, and, when the input voltage Vin is smaller than the threshold voltage Vhv of the light-emitting diode, the light-emitting diode is turned off. The ON period is Ton and the OFF period is Toff. Every two ON periods Ton are spaced by one OFF period Toff, such that the light-emitting diode may flicker when the input voltage Vin varies and make people feel uncomfortable.
On the other hand, due to the limited light-emitting properties of the light-emitting diodes, a portion of the input voltage Vin is consumed on components other than LED (i.e., the region Z with slant lines) and thus this causes a low luminous efficiency of LED.